In the above command, -it means run the container interactively;
-v$PWD:/work means mount the current directory ($PWD will expand
to current absolute path in Linux) under /work in the container.
paddlepaddle/paddle to specify image to use; finnally
/work/train.py is the command to run inside docker.

Also, you can go into the container shell, run or debug your code
interactively:

You can create a container serving PaddlePaddle Book using Jupyter Notebook in
one minute using Docker. PaddlePaddle Book is an interactive Jupyter Notebook
for users and developers.If you want to
dig deeper into deep learning, PaddlePaddle Book definitely is your best choice.